A nonaqueous secondary battery utilizing lithium (lithium secondary battery) is composed of positive and negative electrodes containing a material capable of intercalating and deintercalating lithium, a nonaqueous electrolytic solution (i.e., a nonaqueous liquid electrolyte) containing a lithium salt, and members for holding or separating these parts. The lithium secondary battery is characterized by a high voltage and a high capacity because lithium, which carries electric charges, is light and has an extremely negative potential. However, to have a large quantity of energy stored means to have a great force of destruction in case of runaway of the battery reaction. Therefore security of battery safety is one of the most important subjects in the art. In order to secure safety under conditions of practical use, countermeasures against abnormalities that have been put into practice to date include a porous separator provided between positive and negative electrodes which cuts off an electric current at or above a certain temperature; a safety valve which relieves pressure in case of increase of the internal pressure due to an abnormal reaction, etc.; and a mechanism for cutting an electric current synchronously with the movement of the safety valve (as described in U.S. Pat. No. 4,943,497).
However, there has been a constant demand for a further increased battery capacity, and development of a further improved safety mechanism has been demanded. An attempt is described in JP-A-9-106835 (the term "JP-A" as used herein means an "unexamined Japanese patent application"), in which a battery is protected from destruction by using a compound capable of electrochemically polymerizing at an abnormally high voltage in case of an overcharge thereby to increase the electric resistance of the electrolytic solution. The compounds disclosed include aromatic compounds such as biphenyl, thiophene, and furan. However, these compounds involve the problem that the battery capacity decreases as the amount of the compound increases.